Melanotan I vs Melanotan II: A Question of Receptor Selectivity
By Peptura Research Team/17 May 2026/7 min read
The Melanocortin Receptor Family
The melanocortin family runs to five G protein-coupled receptors: MC1R, MC2R, MC3R, MC4R, and MC5R, each with its own tissue distribution and role. MC1R sits mainly on melanocytes and drives eumelanin synthesis. MC2R is confined to the adrenal cortex and answers to ACTH. MC3R and MC4R are central-nervous-system receptors bound up with energy homeostasis, sexual behaviour, and inflammation control. MC5R turns up in exocrine glands and immune cells. Melanotan I and Melanotan II are both synthetic α-MSH analogues, but they differ sharply in which of these they activate.
Melanotan I: Narrow and Selective
Melanotan I, also called Afamelanotide or NDP-α-MSH, is a 13-amino-acid linear peptide close in structure to α-melanocyte-stimulating hormone, carrying two deliberate substitutions: D-Phe at position 7 and Nle at position 4. These guard against proteolytic degradation and sharply raise MC1R binding affinity. The result is strong selectivity for MC1R over the rest of the family, giving mainly melanogenic effects in research models without much central-nervous-system or appetite-modulating activity.
Melanotan II: Broad Across the Family
Melanotan II is a cyclic heptapeptide α-MSH analogue with a wider grip on the melanocortin family. It activates MC1R for melanogenesis, MC3R and MC4R for central effects on appetite, energy expenditure, and sexual behaviour, and MC5R for exocrine function. The cyclic structure stabilises the peptide and raises potency, but it trades away the MC1R selectivity of Melanotan I, so research models using it show effects across several receptor systems at once.
Why Selectivity Matters
That selectivity gap carries straight into experimental design. Anyone isolating MC1R-driven melanogenesis will pick Melanotan I to keep MC3R, MC4R, and MC5R activation from confounding the readout. Anyone probing central appetite regulation or sexual behaviour through MC3R and MC4R will reach for Melanotan II, or for a more selective MC4R agonist such as PT-141. Despite the shared branding, the two are not interchangeable at the bench.
Research Background
Both compounds trace back to the University of Arizona in the 1980s, developed under principal investigators Hadley and Hruby as melanocortin receptor research tools and potential clinical agents. Melanotan I, as Afamelanotide, has since gained clinical approval in some jurisdictions for erythropoietic protoporphyria. Melanotan II has stayed within research applications. Neither is approved for human use in the UK by the MHRA.
Laboratory Handling
Both come as lyophilised powder. Store at -20°C before reconstitution. Reconstitute with bacteriostatic water by running the diluent slowly down the side of the vial. Keep reconstituted solutions at 2-8°C and use within four weeks, shielding them from prolonged light during handling.
Sourcing in the UK
Peptura supplies research-grade Melanotan I 10mg and Melanotan II 10mg with full third-party Certificate of Analysis published on every product page. Same-day UK dispatch on orders placed before 2pm GMT. For in-vitro laboratory research use only.
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Disclaimer: This article is for research and educational purposes only. All information provided is not intended as medical advice. Peptura products are not for human consumption and are sold strictly for laboratory research use only.